This project aims to investigate the histochemical and physiological properties of masticatory muscles in the adult rat. Although they have been studied less intensely than limb muscles, results of histochemical studies of the muscles of mastication differ in three distinct ways: (1) the masticatory muscles show no fiber type localization within the muscle, (2) there appears to be little cross species uniformity and (3) the muscle fibers observed are strongly suspected to be intrinsically different from limb muscles. Using a detailed and quantitative analysis of the histochemical and immunohistochemical properties of selected masticatory muscles the similarities and differences between limb and jaw muscles will be examined. The mechanical properties of motor units in masticatory muscles have not been studied. The significance of histochemical fiber types in the regulation of movement was apparent for lib muscles only after correlation to motor unit physiological profiles. It is proposed that using individual motor unit glycogen depletion and serial histochemical analyses the organizational principles established for limb muscles will be extended to include those of the masticatory system. Finally by observing limb and jaw muscles following transfer to the counterpart's recipient site and anastomized to foreign neural input the roles played by motorneuron activity and intrinsic properties in regulation will be delineated. Adaptation of these muscles to function, surgery or injury will be better understood.